Solar energy collators have been used for many years as a source of renewable energy using solar irradiation, otherwise known as insolation, to heat a fluid passing over a surface or through a conduit, or to provide solar insolation to other devices that collect heat for useful purposes. The collectors are typically supported directly above a roof and are angled by virtue of their mounting, or include frames to angle the collectors appropriately above a horizontal surface. A challenge in this field is to achieve a highly efficient conversion of solar radiation to thermal energy and to increase the temperature of the fluid to an extent that ensures the utility of the fluid is improved for various energy consuming processes.
Solar thermal collection systems typically perform poorly in winter, late autumn and early spring, when users generally seek to consume more or need the most heat for heating systems. The performance of existing solar thermal collection systems is degraded further in the presence of cloud cover, more common in cooler months. In summer, when demand for heat is reduced because of lower losses to ambient in commercial applications, and/or reduced usage of heat in domestic applications, solar thermal collectors perform most effectively, collecting excess heat energy compared with demand.
Typically, there is an excess capacity of summer heating in fixed solar thermal collectors, and a deficit of heat production in colder months. Where sufficient collectors are deployed in a particular setting for collection of heat in cold months, excess heat must be rejected in the warmer months.
The performance of fixed solar thermal collectors in cooler months is also degraded in that the heat output is at a lower temperature, such that the output is not at a sufficient temperature to meet the consumption requirement.
In addition, many apparatus are empirically positioned, namely, with the same collector position and orientation notwithstanding factors such as the time of year. Such apparatus are directed generally towards the incoming solar radiation at peak summer periods. Accordingly, such apparatus are not designed to compensate for the diurnal changes of the sun and variation in the solar azimuth angle throughout the year, that is unless they are physically re-oriented throughout the year. Furthermore, most existing apparatus known to the Applicant use only the upper surface of a collector panel to collect or utilise the solar radiation. Accordingly, the existing apparatus are not particularly efficient in utilising the incoming insolation, which contributes to the aforementioned problems, particularly during the cooler months when the sun is lowest above the horizon.
Attempts to address the above problems have largely been unsuccessful to date. For example, installing more solar collectors for increased production of hot water in winter requires a higher capital cost, and represents a commercially infeasible solution compared to alternate heating methods. An additional problem is the difficulty and expense associated with heat rejection of excess heat collected in summer.
Installation of moving collectors of concentrators to improve winter performance, and allow any necessary redaction in summer heating performance by “de-tuning” of summer thermal collection, has also been attempted. However, this greatly increases the complexity and expense of the systems, and reduces their commercial value, again rendering this a non-commercial solution.
Installation of a heat store able to store heat for up to 5 years, to allow summer time collection and winter time utilization of solar thermal sourced heat has been developed in at least one location in Northern Canada. This solution requires a “whole of village” development, as smaller sized in-ground heat stores are not practicable. This solution is largely impractical as a retrofit installation since extensive pipework is required between the large central heat store and the consumers of energy in other buildings.
There has also been development of apparatus incorporating reflector panels positioned relative to the collector to provide solar energy to the collector not only from direct solar radiation but from reflected radiation via the reflector panels. However, apparatus of this type that are known to the Applicant still employ an empirical design suited to improving efficiency at one particular time of year, that is, they do not include collectors and reflectors oriented relative to one another specifically to ensure optimal performance throughout the year for a given latitude. Accordingly, known apparatus employing reflective panels, whilst successful in increasing efficiency at certain times of day at a particular time of year, still suffer the same performance problems associated with non-reflector collectors at other times of year.
In addition to problems associated with the operation of existing solar energy collection apparatus, the Applicant has also recognized the need to address problems associated with the design of such apparatus. There is no current method known to the Applicant which provides a means of designing a solar energy collection apparatus and in particular an orientation of a collector and one or more reflectors of the apparatus for optimal performance over a selected time of year (or year round) based at least on latitude. Indeed, there are a number of other factors which may influence the design of such apparatus. For example, a large variety of existing rooflines and orientations are typically encountered. In addition, buildings at different latitudes may require a different orientation of systems to achieve optimum performance. In some installations, wintertime heat collection is most important, while summertime heat collection must be reduced to avoid excess energy accumulation. In other installations, maximum energy collection ever the annual cycle is desirable, while in a further scenario, maximum summertime gain is desired. In other situations, the collection space may be restricted and maximum energy collection per square meter is desired.
The object of this invention is to provide a solar energy collection apparatus and design method that alleviates the above problems, or at least provides the public with a useful alternative.